I noticed this error during a deployment of numerous servers that were configured with litespeed, postgreSQL, and ruby. The installation process was to install ruby, install ruby gems, install postgreSQL, install litespeed, and then sync up the web directory using SVN. After doing so connect via a browser to the server to test things out. On one server I was getting a “503 Service Unavailable” error. The lshttpd(litespeed) logs looked like the below example.

After a bit of searching I pinned the issue down to having missed installing one of the ruby gems. If you are in this situation use the “gem list” command to list all of the gems on the server and make sire that you are not trying to load gems that are not installed. Once the missing gem was installed there were no more 503 errors and things were rocking.